Electrical lead

ABSTRACT

An electrically conductive member ( 10 ) includes an elongate body ( 11 ) which has at least one electrically conductive region ( 20 ). The electrically conductive region ( 20 ) comprises a porous polymeric material coated with an electrically conductive material. A method of manufacturing the electrically conductive member ( 10 ) includes the steps of extruding an elongate body of polymeric material wherein at least one region of the elongate body is porous in nature; and coating said elongate body with an electrically conductive material such that the electrically conductive material substantially coats the pores of said at least one region.

RELATED APPLICATION INFORMATION

This application is a national phase application under 35 U.S.C. §371 ofPCT International Application Serial No. PCT/AU01/01339, filed Oct. 19,2001, published in English, which claims priority to AustralianProvisional Patent Application Serial No. PR0903 filed Oct. 20, 2000.

FIELD OF THE INVENTION

The present invention relates to medical electrical leads and electrodesand in particular to medical leads having electrodes made from ametal-coated polymeric material.

BACKGROUND ART

Electrical leads and electrodes are commonly utilised in the medicalfield for applications such as stimulation, sensing, ablation anddefibrillation.

Traditionally, medical electrodes comprise machined metal or coiledmetal wire components which, while suitably conductive, do not providethe flexibility in both design and mechanical properties afforded by ametal coated polymer. Furthermore, metal coated polymers areparticularly suitable for use in larger area electrodes where theirlight weight, flexibility and versatility are key advantages.

The use of metal coated or metal filled polymers as medical electrodeshas been considered. For example, in U.S. Pat. No. 5,279,781, a metalfilled fibre for use as a defibrillation electrode is described. Themetal in this case is added during the spinning process. To render theelectrode suitably conductive, however, requires the addition of asignificant proportion of metal to the fibre which in turn has anadverse effect on the mechanical strength of the electrode.

Further structures, including metal filled silicones and intrinsicallyconductive polymers, have been considered for use as medical electrodesalthough it has been found that such structures do not have the requiredlevel of conductivity necessary for the abovementioned medicalapplications.

Typically, the problem encountered with using a polymeric material as anelectrode is that it is difficult to obtain a good electrical connectionto the electrode. In U.S. Pat. No. 5,609,622, an electrical connectionwas achieved by utilising an electrode having metal wires embedded inits wall. The electrode was then subjected to an ion beam treatment withmetal such that the metal was deposited within the wall and thereforecontacted the wires. In this case, however, the electrical connectionwas only shown to occur at one end of the electrode and further, it isquestionable whether a good connection is achieved by this method as itrelies upon the incidence of metal contacting wire through the thicknessof the plastic.

The present invention provides an electrical lead and/or electrode whichovercomes the problems of the prior art.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

DISCLOSURE OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

According to a first aspect, the present invention is an electricallyconductive member including an elongate body, the body having at leastone electrically conductive region, the region comprising a porouspolymeric material coated with an electrically conductive material.

Preferably, the electrically conductive member is adapted for medicaluse and in particular, but not limited to, use in cardiac mapping,defibrillation or pacing, neurological applications including neuralstimulation implants, muscle stimulation, sensing and ablation.Accordingly, in a preferred embodiment, the electrically conductivemember may comprise part of a lead or any other form of carrier.

Typically, the electrically conductive member is an elongate tube. Whilethe entire length of the member may be made from a porous polymer coatedwith an electrically conductive material it is also envisaged that theelectrically conductive member may comprise a plurality of distinctelectrically conductive regions made up of the coated porous polymer.

In the embodiment wherein the electrically conductive member is tubular,it is preferred that the pores of the at least one electricallyconductive region are present substantially across the diameter of aside wall of the tubular structure. Accordingly, in this embodiment,electrical connection may be made from internal a lumen of the tube. Itis further envisaged that electrical connection may be made from withinthe side wall of the tube as further discussed below.

Rather than a tube, the electrically conductive member may comprise asolid cylindrical member. In this embodiment, it is again preferred thatthe pores of the at least one electrically conductive region are presentsubstantially across the diameter of the cylindrical member.

In a preferred embodiment, the pores of the polymeric material of the atleast one electrically conductive region are greater than 5 microns andpreferably between 30 and 100 microns. When the porous polymericmaterial is coated with an electrically conductive material, saidelectrically conductive material preferably coats and lines at leastsome of, and preferably all of, the pores.

Typically, the electrically conductive material is a metal and,preferably, a biocompatible metal such as platinum. It is envisaged thata combination of two or more metals or metal alloys may be used,however, to improve electrical conductivity. For example, it may bedesirable to provide a first layer of copper or silver or any othersuitably conductive metal and a second layer of platinum to enable useof the electrically conductive member within a body.

The coating of the porous polymeric material preferably creates asuitably thick layer of metal coating across the at least oneelectrically conductive region. Preferably, the resistance of thecoating is less than 100 ohms and more preferably less than 10 ohms.

The porous polymeric material may be expanded polytetrafluoroethylene(PTFE) wherein the pore size is adjusted to allow the metal coating topenetrate the pores and to produce a coating of sufficient thickness toprovide adequate electrical conductivity. Other materials are envisagedincluding, but not limited to, porous silicones, porous polyurethanes,polyether block amide (PEBAX) or nylon. In each case, the pore size maybe varied depending upon the method of formation of the porous materialor by the addition of additives such as sodium chloride (NaCl), sodiumbicarbonate (Na₂HCO₃) or polyglycolide which can be leached outfollowing moulding or extrusion leaving a porous structure.

Alternatively, the pores of the polymeric material may be formed bydrilling into the polymer using a laser drill. This has the particularadvantage of enabling only a portion of the polymer to be of a porousnature.

The at least one electrically conductive region may be electricallyconnected to an electrical conductor.

In one embodiment, the electrical conductor is a straight or coiledwire, or number of wires, embedded within the body of the electricallyconductive member and preferably within the at least one electricallyconductive region of the member. If the electrically conductive memberis a solid cylindrical member, the wire or wires may be coiled in ahelical manner within the at least one electrically conductive region.If the electrically conductive member is a tubular structure, the wireor wires may be coiled in a helical manner within the wall of the tubeand preferably within the at least one electrically conductive region.In either embodiment, the wire(s) may extend through several pores ofthe at least one electrically conductive region. Accordingly, when theporous polymeric material of the at least one region is coated with theelectrically conductive material, the portions of wire which extendthrough the pores may be simultaneously coated with the electricallyconductive material thereby creating a good electrical connectionbetween the electrical conductor and the electrically conductive region.

The wires may be single wires or multifilament wires. Further, the wireor wires may be made of copper preferably coated with a noble metal suchas palladium or platinum for corrosion resistance. Alternatively, theindividual wires may be a multifilament stainless steel wire. Othersuitable materials include, but are not limited to, platinum or platinumalloy, MP35N or Elgiloy.

In the above embodiment, depending upon the application of theelectrically conductive member, the wire(s) may be connected by aninsulated conductor to either a source of electricity or to an analysermeans. Typically, the wire(s) are connected to the insulated conductorby way of welding. Alternatively, they may be connected by electricallyconductive adhesives or by soldering.

In a further embodiment, the electrical conductor is located internalthe elongate body of the electrically conductive member. For example, ifthe electrically conductive member is a tube having at least oneelectrically conductive region, the electrical conductor may bepositioned within the lumen of the tube. In this embodiment, theelectrical conductor is preferably adapted such that it engages theinternal surface of the tube. To ensure that the electrical conductorengages the tube, it is preferred that the electrical conductorcomprises a resilient spring, such as a spiral spring that, oncepositioned in the tube, can expand into contact with the inner wall ofthe tube.

In another embodiment, the electrical conductor may be a spring formedfrom a shape memory alloy such as Nitinol™. The shape memory springpreferably moves, when exposed to a pre-determined temperature, from afirst position to a second position wherein when in the second position,the spring expands such that it has an outer diameter greater than theinner diameter of the tube. Accordingly, when internal the lumen of thetube and when in the expanded second position, the spring engages theinner surface of the tube to a sufficient extent to provide a goodelectrical connection between the electrical conductor and the at leastone electrically conductive region.

In one embodiment, the shape memory alloy spring expands into contactwith the inner surface of the tube upon exposure to body temperature.

The shape memory spring may be connected to an insulated conductor bywelding, the use of electrically conductive adhesives or soldering.

In the above embodiments, it is preferred that the electrical conductorsuch as the wire(s) embedded within the electrically conductive memberor a shape memory alloy spring positioned within a lumen of a tubularelectrically conductive member, extends the entire length of theelectrically conductive member, or at least the length of the at leastone electrically conductive region, such that a good electricalconnection between the electrical conductor and the at least oneelectrically conductive region can be made.

In another embodiment, the electrical conductor is adapted to engage anend of the electrically conductive member. For example, the electricalconductor may include a shape memory alloy tube that is adapted toexpand and increase its internal diameter upon heating above apre-determined temperature or exposure to a particular pre-determinedtemperature. The shape memory alloy tube may then be slid over an end ofthe electrically conductive member. Upon heating above or cooling belowthe pre-determined temperature depending on the type of shape memoryalloy, the shape memory alloy tube preferably returns to its originalunexpanded shape therefore effectively clamping down on an end of theelectrically conductive member. This embodiment provides a uniformradial pressure on the end of the member and provides a good electricalconnection between the electrical conductor and the at least oneelectrically conductive region of the member. If the electricallyconductive member is a tube, it may be necessary to provide an innertube which is relatively stiff and which may be positioned internal thelumen of the tube to prevent collapse of the member.

In a second aspect, the present invention consists in a method ofmanufacturing the electrically conductive member of the first aspect,said method comprising the steps of:

(i) extruding an elongate body of polymeric material wherein at leastone region of the elongate body is porous in nature; and

(ii) coating said elongate body with an electrically conductive materialsuch that the electrically conductive material substantially coats thepores of said at least one region.

While the entire length of the elongate body may be coated with theelectrically conductive material, in the embodiment wherein there aredistinct regions of porous polymeric material, it may be preferred thatonly the distinct porous regions are coated with said electricallyconductive material rather than the entire length of the elongate bodywhich may include non-porous regions.

Where the electrical conductor comprises a straight or coiled wire, theelectrically conductive member may be manufactured in a number ofstages. For example, a first tube, or layer, or solid cylindrical membermay be formed from either a porous polymeric material or non-porouspolymeric material or a combination thereof. The wire may then bewrapped around and along at least a portion of the first tube or solidcylindrical member in a helical manner or extended along at least aportion of the length of the first tube or layer or solid cylindricalmember. The wire and the first tube or layer or solid cylindrical membermay then be overlaid with a coating or another layer. The coating or theother layer may be a porous polymeric material or alternatively, apolymeric material having regions which are of a porous nature. In oneembodiment, the coating may be a second tube.

In a further embodiment of the second aspect, the electricallyconductive member may comprise a tube. In this embodiment, theelectrical conductor is positioned within the lumen of the tube. Theelectrical conductor is preferably positioned such that it engages theinternal surface of the tube. To ensure that the electrical conductorengages the tube, it is preferred that the electrical conductorcomprises a resilient spring, such as a spiral spring that, oncepositioned in the tube, can expand into contact with the inner wall ofthe tube.

In another embodiment of the second aspect, the electrical conductor canbe formed in a spring form from a shape memory alloy such as Nitinol™.The shape memory spring can preferably move from a first position to asecond position wherein when in the second position, the spring couldexpand such that it had an outer diameter greater than the innerdiameter of the tube.

The electrical conductor may be adapted to engage an end of theelectrically conductive member. For example, the electrical conductormay include a shape memory alloy tube that is adapted to expand andincrease its internal diameter upon heating above a pre-determinedtemperature. The shape memory alloy tube may then be slid over an end ofthe electrically conductive member. Upon heating above or cooling belowthe pre-determined temperature depending on the type of shape memoryalloy, the shape memory alloy tube preferably returns to its originalunexpanded shape therefore effectively clamping down on an end of theelectrically conductive member. This embodiment provides a uniformradial pressure on the end of the electrically conductive member andprovides a good electrical connection between the electrical conductorand the at least one electrically conductive region of the member.

Typically, the electrically conductive material is applied to theelongate body or preferably to the at least one electrically conductiveregion using a wet technique such as electroless plating. In thisembodiment, the electrically conductive material may be forced throughthe pores of the at least one electrically conductive region by theapplication of pressure.

Alternatively, the electrically conductive material may be applied byelectroless plating followed by the additional step of electroplating.

Each of the above processes preferably ensures that a coating ofelectrically conductive material penetrates substantially all the poresof the electrode. If the at least one region of electrically conductivematerial has pores disposed substantially throughout the entirethickness of said region, it is envisaged that electrical connection maybe made by way of an electrical conductor, as described above, eitherwithin the wall of the elongate body or on the inside of the elongatebody (for example if the elongate body is a tubular structure).

The process of coating the elongate body with an electrically conductivematerial such that the pores of the at least one electrically conductiveregion are coated with such a material may involve a number of stepsprior to the actual coating with the electrically conductive material.The steps include:

(1) Cleaning.

(2) Surface Modification.

(3) Catalysis.

(4) Coating.

(1) The material to be coated is typically washed in an organic solventsuch as acetone or ethyl acetate or in a solution containing a suitablesurface active agent. Usually some agitation is required such as from anultrasonic cleaner or a shaker water bath. The step of cleaning may becarried out above room temperature.(2) The step of surface modification results in a more wettable orhydrophilic surface such that the deposition of the coating may beaccelerated and, further, chemical and mechanical adhesion of thecoating to the surface may be improved.

Chemical adhesion may be improved by creating the most suitablefunctional groups on the surface of the polymer such as amides, whilemechanical adhesion may be improved by creating a roughened surfaceusing chemical (etching) or mechanical (sandblasting) methods.

Typically, the surface modification chemicals are infused into the poresusing pressure via a pump or syringe. Alternatively, the porous materialto be coated may be placed in the treatment solution and evacuated in avacuum thereby removing gas bubbles from within the porous structureresulting in contact of all surfaces with the treatment solution.

Additionally, plasma treatment may be used to improve wettability and/orimprove chemical or mechanical adhesion.

Following this step, the structure to be coated is rinsed several timespreferably in deionised water.

(3) The catalyst step results in the deposition of a small amount ofnobl metal on the surface of the material. This provides the sites fordeposition of the coating material, for example, platinum. While typicalelectroless plating uses a tin/palladium catalyst it is preferred that aprocess which eliminates the tin is used. For example, palladium in anacidic aqueous solution or dimethyl sulfoxide both of which can bereduced in a hydrazine solution is preferred. The latter is particularlyuseful as, being an organic solution, it allows improved wettability formany substrates.

In one embodiment of the catalysis of a material such as silicone, thecatalyst, in the form of palladium metal powder can be mixed into asilicone dispersed in a solvent and then infused into the pores andcured prior to coating. In this embodiment, a small concentration ofactual silicone is required so as to provide a thin layer on the surfaceof the pores rather than fill the pores with silicone. The palladiummetal will act as a catalyst and will be bound to the silicone andtherefore increase the adhesion of the coating material which issubsequently applied.

Alternatively, the silicone mix may be infused with palladium prior tomoulding or extrusion.

The catalyst step may be performed a number of times.

(4) The coating process preferably uses electroless plating wherein anumber of metals may be deposited using either commercially available orcustom made solutions of complex metal ions together with a stabiliserand an added reducer. The solution typically allows controlleddeposition of a metal over a specific period of time. If a biocompatibleelectrode is required, it is preferred that the metal is platinum.

A fifth step may be added to the above process if a thicker coating ofmetal and therefore higher conductivity is required. This would involvefurther electroless plating or electroplating.

In a further embodiment, following the process of coating, the pores areinfused with a liquid adhesive such as, but not limited to, a siliconedispersant to effectively seal the pores. Preferably the infusion of theadhesive is carried out from within the electrically conductive memberwhen said member is a tubular structure. This embodiment has theadvantage of enabling an electrically conductive member to be implantedin a body for long periods of time with minimal tissue ingrowth into themember. This facilitates easy removal of the member if required.

In a third aspect, the present invention consists in an electricallyconductive member including an elongate body, said elongate body havingat least one electrically conductive region comprising a polymericmaterial together with at least one electrical conductor wherein atleast a portion of the polymeric material and at least a portion of theat least one electrical conductor have a coating thereon of anelectrically conductive material.

Preferably, the elongate body comprises a tubular body made of asuitable polymer material. The electrical conductor is preferably housedwithin at least part of a side wall of the tubular body. In addition tobeing housed within a side wall of the tubular body at the at least oneelectrically conductive region of the body, the electrical conductor mayextend along the entire length of the tubular body.

The elongate body preferably comprises a first cylindrical inner memberand a second outer member, said second outer member substantiallyforming a coating around the first inner member. The second outer memberpreferably extends over the entire length of the first inner member. Theat least one electrical conductor is preferably sandwiched between thefirst inner member and the second outer member.

The first inner member may be made from a suitable polymeric materialsuch as polyurethane, polyether block amide (PEBAX), PEEK or polyimide.The second outer member is preferably formed from a similar polymericmaterial to that of the first inner member. Further, it is preferredthat the second outer member is made from a transparent or at leastsubstantially transparent material such that the at least one electricalconductor may be viewed through the second outer member.

Preferably, the second outer member is much thinner than the first innermember and typically, the second outer member is sufficiently thick toonly just cover the at least one electrical conductor.

The at least one electrical conductor may comprise a metal wire or wiresmade from material such as PFA, polyimide insulated copper wire(s) orcopper alloy wire(s). Preferably, the wire(s) have a diameter ofapproximately 0.025 to 0.3 mm.

Typically, during manufacture, single wires may be wound substantiallyaround the circumference of the first inner member. Preferably, between8 to 24 wires are wound around the first inner member in this mannerwherein each wire has a predetermined spacing between it and the nextwire. Said 8 to 24 wires may form a particular group which is spacedfrom a second or subsequent group of wires by a gap which is preferablylarger than the gap between each wire of each group. In this way,identification of each group may be more easily determined. To aididentification, each group may further be colour coded.

The at least one electrical conductor may be helically wound around thefirst inner member. However, the present invention is not limited to theparticular arrangement of the at least one electrical conductor and anumber of combinations and orientations are envisaged.

Preferably at least one portion of the at least one electricalconductor, is not overlaid by the second outer member, that is, the atleast one portion is exposed to the outside environment. The at leastone portion of the electrical conductor this embodiment is preferablycoated with the electrically conductive material. It is furtherpreferred that at least a portion of the polymeric elongate bodyadjacent the exposed portion of the electrical conductor is also coatedwith the electrically conductive material.

Typically, a band around the circumference of the elongate body iscoated together with the exposed portion of the electrical conductor toform a band electrode on the elongate body.

Preferably, the electrically conductive material is a metal and,preferably, a biocompatible metal such as platinum. It is envisaged thata combination of two or more metals or metal alloys may be used,however, to improve electrical conductivity. For example, it may bedesirable to provide a first layer of copper or silver or any othersuitably conductive metal and a second layer of platinum to enable useof the electrically conductive member within a body.

It is preferred that the exposed at least one portion of the electricalconductor is protected from corrosion. This may be achieved by, forexample, immersing the elongate body in a solution such as palladiumchloride which will coat the exposed portion(s).

In a fourth aspect the present invention provides a method ofmanufacturing an electrically conductive member, the method comprisingthe steps of:

(i) extruding an elongate inner member from a polymeric material;

(ii) applying at least one electrical conductor to an exposed surface ofthe inner member;

(iii) overlaying the inner member and the at least one electricalconductor with an outer member made from a polymeric material such thatthe at least one electrical conductor is covered by said outer member;

(iv) exposing at least a portion of the at least one electricalconductor; and

(v) coating said exposed portion of the at least one electricalconductor and at least a portion of the outer member with anelectrically conductive material.

Preferably, the inner member is extruded as a tube made from a suitablematerial such as polyurethane or polyether block amide (PEBAX).

The at least one portion of the at least one conductor may be exposed bya number of means including, but not limited to, applying heat,chemicals or lasers to remove the area of the outer layer covering theat least one portion. Desirably, a laser technique is used (eg quadrupleYag laser) as such a technique provides good accuracy. For example, thelaser beam is capable of following a particular path of, say, ahelically wound wire acting as the at least one electrical conductor.While, only a small portion of the at least one conductor may be exposedin this manner, the present invention is not limited to the amount ofconductor exposed and, indeed, the entire conductor may be exposed.

For high energy applications, such as radio frequency (RF) or microwaveablation, adjacent electrical conductors may be exposed and coated withelectrically conductive material to form a single electrode. Such aconfiguration decreases the current density. The electrical conductorsof this embodiment may be electrically connected to each other at aproximal end of each electrical conductor. The number of electrodesformed together with the spacing between each electrode may be varied.

The exposed portion of electrical conductor(s) may be protected fromcorrosion by immersion in an acidic solution of, for example, palladiumchloride, which will coat all the exposed portions.

It is desirable that the at least one portion of the at least oneelectrical conductor and at least a portion of the elongate body whichtogether are coated to form an electrode are catalysed. To preventcatalysis of the remainder of the elongate body or electrical conductorwhich form a non-electrode area, these areas are protected fromcatalysis by masking them by, for example, photolithography or by usingpieces of heat shrink tubing such as PET to protect said areas. Analternative to masking is the use of an ink which is pad printed overthe areas to be coated and thus the areas which are to become theelectrodes. The ink used may, or may not be electrically conductive butin any event should be able to catalyse a subsequent plating step. Ifradio opacity is required it may be desirable to use an ink includingcolloidal palladium or silver.

The catalyst step results in the deposition of a small amount of noblemetal on the surface of the material to be coated. This provides thesites for deposition of the electrically conductive material, forexample, platinum. While typical electroless plating uses atin/palladium catalyst it is preferred that a process which eliminatesthe tin is used. For example, palladium in an acidic aqueous solution ordimethyl sulfoxide both of which can be reduced in a hydrazine solutionis preferred. The latter is particularly useful as, being an organicsolution, it allows improved wettability for many substrates.

The catalyst step may be performed a number of times.

The coating process preferably uses electroless plating wherein a numberof metals may be deposited using either commercially available or custommade solutions of complex metal ions together with a stabiliser and anadded reducer. The solution typically allows controlled deposition of ametal over a specific period of time. If a biocompatible electrode isrequired, it is preferred that the metal is platinum.

If relatively thick coatings are required, it is preferred that a porouspolymer is used.

The electrodes formed with respect to the third and fourth embodiments,may be protected by a layer of, for example polyethylene glycol ormannitol. Such a protective layer preferably allows an electrical chargeto pass therethrough.

The following examples describe the preparation of the electrodeaccording to several embodiments of the first and second aspects of thepresent invention.

EXAMPLE 1

A porous polyurethane tube was made using a spraying system. Firstly awire mandrel was connected to an electrical motor using a chuck. Thewire was the simultaneously coated with a mixture of polyurethane(Pellethane) dissolved in dimethylformamide (1% polyurethane) and water.The water polymerised the polyurethane prior to deposition creating aporous layer. A copper wire was then wound onto the coated mandrel and afurther layer was uniformly coated with the mixture of polyurethanedissolved in dimethylformamide and water. The spraying continued untilthe appropriate diameter was achieved ie. 2.2 mm (this was chosen asonce assembled into a lead, a 2.2 mm lead body would comfortably passdown a 7 French introducer).

The porous component was then coated with platinum using the normalcleaning, surface modification, catalysis and coating steps previouslyoutlined.

The resistance was then measured to be approximately 0.5 Ω for a 1 cmlength of the porous component, and approximately 1 Ω from the end ofthe copper wire to the surface of the component.

EXAMPLE 2

An expanded PTFE tube was supplied by Impra which had a pore size of 30microns. The tube was immersed in alcohol and placed in an ultrasoniccleaner to remove air bubbles and wet the surface.

The sample was removed from the alcohol and etched for 1 minute withFluoroEtch from Acton. A syringe was used to try and force the solutionthrough the pores however this was unsuccessful.

The tube was then catalysed using a 2 g/l solution of PdCl₂ in DimethylSulfoxide for 5 minutes intermittently attempting to force the solutionsthrough the pores. This was followed by a reduction step in 4% Hydrazinesolution.

The catalysed tube was then electrolessly coated using a platinumcomplex solution and hydrazine.

After 1.5 hours the sample was a shiny, metallic colour on the outside.

After drying, the resistance along the surface was found to beapproximately 20 Ω for a 1 cm length, however the resistance through thethickness varied from 25-50 Ω.

EXAMPLE 3

Another expanded PTFE tube was supplied by Impra however this time thepore size was increased to 90 microns. The tube was immersed in alcoholand placed in an ultrasonic cleaner to remove air bubbles and wet thesurface.

The sample was removed from the alcohol and etched for 30 seconds withFluoroEtch from Acton. A syringe was used to try and force the solutionthrough the pores. This time the solution was able to freely passthrough the structure.

The tube was then catalysed using a 2 g/l solution of PdCl₂ in DimethylSulfoxide for 5 minutes intermittently forcing the solutions through thepores. This was followed by a reduction step in 4% Hydrazine solution.

The catalysed tube was then electrolessly coated using a platinumcomplex solution and hydrazine intermittently forcing the solutionthrough the pores

After 1.5 hours the sample was a shiny, metallic colour on the outside.

After drying, the resistance along the surface was found to beapproximately 1.5 Ω for a 1 cm length. The resistance through thethickness was approximately 1.5 Ω. No materials were removed using astandard tape test to measure adhesion.

A 4 mm length was then cut and a 2.1 mm diameter Nitinol™ spring (fromMicrovena, White Bear Lake Minn. USA) was straightened and passed up themiddle of the cut platinum coated tube. The structure was then placed inthe oven at 70° C. and the Nitinol™ spring went back to its originalshape clamping on the inside of the platinum coated tube.

A length of 0.2 mm diameter copper wire was then welded to one end ofthe Nitinol spring. The resistance was found to be 1.8 ohms from the endof the copper wire and the outside of the platinum coated expandedTeflon.

A PEBAX tube was passed over each end of the spring and then glued withepoxy forming a butt joint on each side of the platinum coated expandedTeflon component.

After curing the lead was then tested in an isolated cow heart, byimmersing the heart with electrode attached into a conductive media andRF energy passed through the electrode to the heart creating lesions.The test device produced similar lesions to a commercially availableablation lead.

The same lead was tested when delivering pacing pulses and a suitableimpedance resulted.

Due to flexibility and versatility the electrodes can be made differentshapes, sizes, numbers and spacing. This is important when designing newleads for various applications eg ablation leads for treating atrialfibrillation.

The following examples describe the preparation of the electrodeaccording to several embodiments of the third and fourth aspects of thepresent invention.

EXAMPLE 4

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg.The cable contained 8 insulated wire coils in the wall of the tube. Theinsulating layer was made from a thin layer of PEBAX. Over one of thewires, a 4 mm length of insulation was removed to expose thecorresponding amount of wire. A 4 mm band of the cable around theexposed wire was masked. Some plateable conductive ink from CreativeMaterials (CMI 117-31) Tyngsboro Mass. was coated around the unmaskedregion covering the exposed conductor. The electrode with ink was thenimmersed in a platinum complex electroless bath and coated for 1 hour at60 deg C. using Hydrazine as the reducer resulting in a thickness of 0.5microns. The pacing impedance of the plated electrode was then measuredin a 0.18% NaCl solution using a nickel plate as the return electrode.The pacing pulse used was 5 volts and 0.5 ms. The impedance was found tobe 250 ohms. This value was compared to a commercially availableablation electrode which was found to be 180 ohms. No damage to thecoated electrode resulted.

EXAMPLE 5

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg.The cable contained 8 insulated wire coils in the wall of the tube. Theinsulating layer was a thin layer of PEBAX. Over one of the wires, a 4mm length of insulation was removed to expose the corresponding amountof wire. A 4 mm band of the cable around the exposed wire was masked.Some plateable conductive ink from Creative Materials (CMI 117-31)Tyngsboro Mass. was coated around the unmasked region covering theexposed conductor. The electrode ink was coated with a 3 micron layer ofcopper using electroless plating. The copper coated electrode was thenimmersed in an acid palladium chloride solution to catalyse the surfaceand immersed again in platinum complex electroless bath and coated for 1hour at 60 deg C. using Hydrazine as the reducer. The pacing impedanceof the plated electrode was then measured in a 0.18% NaCl solution usinga nickel plate as the return electrode. The pacing pulse used was 5volts and 0.5 ms. The impedance was found to be 120 ohms. This value wascompared to a commercially available ablation electrode which wasmeasure to be 180 ohms. No damage to the coated electrode resulted.

EXAMPLE 6

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg.The cable contained 8 insulated wire coils in the wall of the tube. Theinsulating layer was a thin layer of PEBAX. Over one of the wires, a 4mm length of insulation was removed to expose the corresponding amountof wire. A 4 mm band of the cable around the exposed wire was masked.Some plateable conductive ink from Creative Materials (CMI 117-31)Tyngsboro Mass. was coated around the unmasked region covering theexposed conductor. The electrode ink was coated with a 3 micro layer ofcopper using electroless plating. The copper coated electrode was thenimmersed in an acid palladium chloride solution to catalyse the surfaceand immersed again in platinum complex electroless bath and coated for 1hour at 60 deg C. using Hydrazine as the reducer.

The electrode was then placed on a piece of meat immersed in a 0.18%solution of NaCl and a stainless steel return electrode underneath. Highfrequency RF power was delivered through the electrode for 60 seconds,resulting in a lesion similar to a commercially available ablationelectrode.

EXAMPLE 7

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg.The cable contained 8 insulated wire coils in the wall of the tube. Theinsulating layer was a thin layer of PEBAX. Over one of the wires, a 4mm length of insulation was removed to expose the corresponding amountof wire. A 4 mm band of the cable around the exposed wire was masked.Some plateable conductive ink from Creative Materials (CMI 117-31)Tyngsboro Mass. was coated around the unmasked region covering theexposed conductor. The electrode ink was coated with a 3 micron layer ofcopper using electroless plating. The copper coated electrode was thenimmersed in an acid palladium chloride solution to catalyse the surfaceand immersed again in platinum complex electroless bath and coated for 1hour at 60 deg C. using Hydrazine as the reducer.

The coated electrode was then immersed in a 0.18% NaCl solution using anickel plate as the return electrode. A biphasic defibrillation pulse130 volts in amplitude and 6 ms in pulse width was delivered through thecoated electrode which resulted in no damage to the electrode and animpedance of 130 ohms.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are now described with referenceto the accompanying drawings, in which:

FIGS. 1 a, 1 b and 1 c are side elevational views illustrating theconstruction of one embodiment of the present invention;

FIGS. 2 a, 2 b and 2 c are cross-sectional view through I-I of FIGS. 1a, 1 b and 1 c respectively;

FIG. 3 is a side elevational view of a cut-away portion of an embodimentof the invention;

FIGS. 4 a and 4 b are part cut-away, part side elevational views of afurther embodiment of the invention;

FIGS. 5 a and 5 b are side elevational views of a further embodiment ofthe invention;

FIG. 6 is a schematic view of a multi-electrode assembly incorporatingelectrically conductive regions of the present invention;

FIG. 7 is a perspective view of a number of electrically conductiveregions of the present invention in an electrode assembly;

FIGS. 8 a, 8 b and 8 c are schematic views showing the steps ofmanufacture of an electrically conductive member according to a furtheraspect of the invention;

FIGS. 9 a, 9 b and 9 c are schematic views showing the steps ofmanufacture of an electrically conductive member of another embodimentof the aspect depicted in FIGS. 8 a, 8 b and 8 c; and

FIGS. 10 a, 10 b and 10 c are schematic views showing the steps ofmanufacture of an electrically conductive member of a further embodimentof the aspect depicted in FIGS. 8 a, 8 b and 8 c

DETAILED DESCRIPTION OF THE DRAWINGS

The lead 10 of the present invention includes an elongate body 11 havingat least one electrically conductive region 20 thereof made from aporous polymeric material. The porous polymeric material is coated withan electrically conductive material and preferably a metal such asplatinum.

As discussed above, the lead of the present invention is adapted formedical use and in particular use in cardiac mapping, defibrillation orpacing, neurological applications including neural stimulation implants,muscle stimulation, sensing and ablation.

As depicted in the drawings, the lead 10 has a tubular structure havinga wall 12 and an internal lumen 13. While only one region 20 of the tubemay be made from the porous polymeric material, it may be preferablethat the entire length of the tube is made from said material.

The pores within the wall 12 are preferably greater than 5 microns andpreferably between 30 and 100 microns.

The coating of the porous polymeric material with the metal creates asuitably thick layer of metal coating thereby increasing electricalconductivity through the lead 10.

To establish a good electrical connection the lead includes a conductivemember 14.

In one embodiment, depicted in FIGS. 1 a, 1 b, 1 c, the conductivemember 14 comprises a coiled wire 15 embedded within a wall 12 of thelead 10. The wire 15 is wrapped around and along a substantial length ofthe lead and preferably along the entire lead. While not shown, the wire15 may pass through several pores of the polymeric material and thuswhen the porous polymer is coated with the metal, the portions of wire15 within the pores may simultaneously be coated with the metal therebycreating a good electrical connection between wire and the at least oneelectrically conductive region 20.

As shown in FIGS. 1 a, 1 b and 1 c, the lead of this embodiment may bemade in a number of stages. A first tube 16 is created as shown in FIG.1 a. The tube 16 may, or may not be, porous in nature. The wire 15 issubsequently wrapped around and along the first tube 16 in a helicalmanner and the wire 15 and first tube 16 subsequently overlayed with asecond porous polymer material 17.

In another embodiment, the conductive member 14 is a shape memory alloyspring 18 such as a Nitinol™ spring. The spring 18 of this embodiment ispositioned internal the lumen 13 of the lead 10. In use, the spring 18may be exposed to a pre-determined temperature that causes it to expandsuch that it abuts with the internal surface 19 of the lead 10.Preferably, the spring can normally expand to such an extent that itsexternal diameter is greater than the diameter of the lumen 13 resultingin a good electrical connection between the spring and the at least oneelectrically conductive region.

In another embodiment of the invention depicted in FIGS. 5 a and 5 b,the conductive member 14 is adapted to engage one end 21 of the lead 10.Preferably the conductive member is a shape memory alloy tube 22 whichis adapted to expand and increase its internal diameter upon heatingabove or cooling below a pre-determined temperature depending on thetype of shape memory alloy. The shape memory alloy tube 22 may then beslid over the end 21 of the lead 10. Upon heating up or cooling belowthe pre-determined temperature depending on the type of shape memoryalloy, the shape memory alloy tube 22 returns to its original unexpandedshape therefore effectively clamping down on an end of the lead as shownin FIG. 5 b. Accordingly, there is provided a uniform radial pressure onthe end 21 of the lead 10 which results in a good electrical connectionbetween the alloy tube and the at least one electrically conductiveregion. In this embodiment, it may be necessary to provide an inner,relatively stiff tube (not shown) which may be positioned internal theelectrode 10 to prevent collapse of the lead 10.

Once the lead 10 has been coated with the selected metal, the lead 10may be cut to the desired length depending on the application of theelectrode. For example, a defibrillation electrode formed from the leadmay need to be a length of around 60 mm whereas a lead acting as anelectrode for mapping or sensing need only be a few millimetres inlength.

A multi-electrode system along a lead may be constructed by threadingtogether lengths of coated 23 or uncoated 24 tubes of specified lengthsas depicted in FIG. 6. The coated 23 and uncoated 24 tubes are joinedtogether using butt joints which may have spring or tubing supports (notshown) within the lumen of the tubes 23 or 24.

In the aspect of the invention depicted in FIGS. 8 a, 8 b and 8 c, theinvention consists in an electrically conductive member 30 including anelongate body 31. The elongate body 31 has at least one electricallyconductive region 32 which comprises a polymeric material together 33together with at least one electrical conductor 34. A portion of thepolymeric material 33 and a potion or all of the electrical conductor 34are coated with an electrically conductive material 35.

The elongate body comprises a first cylindrical inner member 36 and asecond outer member 37 said second outer member substantially forming acoating around the first inner member 36. The second outer member 37extends substantially over the entire length of the first inner member36. The at least one electrical conductor 34 is sandwiched between thefirst inner member 36 and the second outer member 37.

As shown in FIG. 8 b, the electrical conductor 34 is exposed. This maybe achieved by a number of means including the application of heat,chemicals or lasers to remove the area of the outer member 37 coveringthe electrical conductor 34.

The exposed electrical conductor 34 and an area of the polymericmaterial 33 adjacent the electrical conductor 34 is then catalysed andcoated with the electrically conductive material 35 to form an electrode38.

As depicted in FIGS. 9 a, 9 b and 9 c, two electrodes 38 may be formedby coating separate electrical conductors 34 together with an adjacentarea of polymeric material 33.

For high energy applications such as RF or microwave ablation, FIGS. 10a, 10 b and 10 c show how a number of electrical conductors 34 togetherwith their adjacent polymeric material 33 may be coated with anelectrically conductive material to form a single electrode 38. Theelectrical conductors of this embodiment may be electrically connectedto each other at a proximal end of each electrical conductor. The numberof electrodes formed together with the spacing between each electrodemay be varied.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A medical use electrical lead comprising: an elongate, cylindricalbody of a polymeric material, the body having a length greater than itsdiameter and the body having at least one electrically conductive regiondefining an electrically conductive surface, the region being defined bya porous polymeric material having a plurality of pores therein, thepores being coated with a coating of an electrically conductivematerial, the coating comprising a first layer of a metal-depositioncatalyst applied to the body and at least one further layer of aconductive material comprising a metal overlying the catalyst, thecoating extending through the pores, wherein the pores extendtransversely to a longitudinal axis of the cylindrical body at leastpartly through material of the cylindrical body; and at least oneelectrical conductor contained in the material of the cylindrical bodyand extending into the at least one electrically conductive region sothat the at least one conductor is in electrically conductivecommunication with the conductive surface of the at least oneelectrically conductive region through the electrically conductivematerial extending through the pores, and forming an electricallyconductive path that forms points of contact between the conductivesurface and the embedded conductor.
 2. The electrical lead of claim 1comprising a plurality of electrically conductive regions.
 3. Theelectrical lead of claim 1 wherein said elongate body is tubular.
 4. Theelectrical lead of claim 1 wherein said elongate body comprises a solidcylindrical member.
 5. The electrical lead of claim 1 wherein the poresof the polymeric material comprising the at least one electricallyconductive region are greater than 5 microns.
 6. The electrical lead ofclaim 5 wherein the pores of the polymeric material comprising the atleast one electrically conductive region are between 30 and 100 microns.7. The electrical lead of claim 1 wherein the electrically conductivematerial comprises at least one metal.
 8. The electrical lead of claim 7wherein the metal is a biocompatible metal.
 9. The electrical lead ofclaim 7 wherein the metal is a combination of two or more metals ormetal alloys.
 10. The electrical lead of claim 1 wherein the porouspolymeric material is expanded polytetrafluoroethylene (PTFE) andwherein the pore size is variable.
 11. The electrical lead of claim 1wherein the porous polymeric material is selected from the groupconsisting of porous silicones, porous polyurethanes, polyether blockamide (PEBAX) or nylon.
 12. The electrical lead of claim 1 wherein thepores of the polymeric material are formed by the addition of additivesselected from the group consisting of sodium chloride (NaCl), sodiumbicarbonate (Na₂HCO₃) or polyglycolide to the polymeric material. 13.The electrical lead of claim 1 wherein the pores of the polymericmaterial are formed by laser drilling the polymeric material.
 14. Theelectrical lead of claim 1 wherein said portion of the electricalconductor which extends through the pores is coated with theelectrically conductive material.
 15. The electrical lead of claim 1wherein the at least one electrical conductor comprises a straight orcoiled wire, or number of wires.
 16. The electrical lead of claim 15wherein the wires are either single or multifilament wires.
 17. Theelectrical lead of claim 15 wherein the wire or wires are made of coppercoated with a noble metal.
 18. The electrical lead of claim 15 whereinthe wire or wires are made from a material selected from the groupconsisting of stainless steel, platinum or platinum alloy MP35N,Elgiloy, copper or silver either alone or coated with another metal. 19.The electrical lead of claim 15 wherein the electrical conductor is aspring wire formed from a shape memory alloy.
 20. The electrical lead ofclaim 19 wherein the shape memory alloy is Nitinol™.
 21. A medical useelectrical lead comprising: an elongate, cylindrical body having alength greater than its diameter and being of a polymeric material, atleast one transversely extending hole being defined at least partiallythrough the polymeric material of the body; at least one electricalconductor contained wholly within the polymeric material of the body inat least a region of the at least one transversely extending hole; andat least one coating of an electrically conductive material applied toan outer surface of the cylindrical body, the coating comprising a firstlayer of a metal-deposition catalyst applied to the body and at leastone further layer of a conductive material comprising a metal overlyingthe catalyst, the coating defining an electrically conductive surfacewhich is in electrical communication with the at least one electricalconductor via the coating being contained in, and extending through, theat least one transversely extending hole defined in the body, so thatthe coating, by extending through the at least one transverselyextending hole forms an electrically conductive path that forms a pointof contact between the electrically conductive surface of the coatingand the at least one electrical conductor to define an electricallyconductive region on the cylindrical body.
 22. The electrical lead ofclaim 21 wherein the elongate body is tubular.
 23. The electrical leadof claim 22 wherein the at least one electrical conductor is containedwithin at least a part of a wall of the tubular body.
 24. The electricallead of claim 21 wherein the elongate body comprises a cylindrical innermember and an outer member arranged about the inner member.
 25. Theelectrical lead of claim 24 wherein the at least one electricalconductor is positioned between the inner member and the outer member.26. The electrical lead of claim 24 wherein the inner member and theouter member are made from a polymeric material selected from the groupconsisting of polyurethane and polyether block amide (PEBAX).
 27. Theelectrical lead of claim 26 wherein the outer member is made from asubstantially visually transparent material.
 28. The electrical lead ofclaim 21 wherein the at least one electrical conductor comprises atleast one metal wire made from a material selected from the groupconsisting of: PFA, FEP, polyimide and polyurethane insulated copperwire(s) or copper alloy wire(s).
 29. The electrical lead of claim 28wherein the at least one metal wire has a diameter of betweenapproximately 0.1 to 0.3 mm.
 30. The electrical lead of claim 28 whereinthe at least one electrical conductor comprises a plurality of wires.31. The electrical lead of claim 21 wherein the coating forms a bandelectrode on the outer surface of the elongate body.
 32. The electricallead of claim 21 wherein the electrically conductive material is atleast one metal selected from the group consisting of: platinum, metalalloys, stainless steel, copper and silver.
 33. The electrical lead ofclaim 21 in which the least one transversely extending hole is alaser-cut hole.
 34. The electrical lead of claim 21 in which theelongate body is configured to be inserted into a patient's body. 35.The electrical lead of claim 21 in which the elongate body is a cardiaccatheter.
 36. The electrical lead of claim 21 in which the at least oneelectrical conductor is an insulated conductor having a conductive coresurrounded by insulation with a part of the insulation of the conductorremoved to form at least a portion of the hole through which theelectrically conductive material passes to make electrical contactbetween the coating and the conductive core.
 37. The electrical lead ofclaim 31 in which the coating is flexible to form a flexible bandelectrode on the outer surface of the elongate body.
 38. The electricallead of claim 31 in which a plurality of band electrodes are arranged inlongitudinally spaced relationship at a distal region of the elongatebody.
 39. The electrical lead of claim 23 which includes a plurality ofelectrical conductors, the electrical conductors being coiled in ahelical manner within the wall of the elongate body.
 40. The electricallead of claim 21 in which the elongate body member is of a non-porousmaterial.
 41. A catheter comprising: an elongate, cylindrical bodyhaving a length greater than its diameter and being of a polymericmaterial, at least one transversely extending hole being defined atleast partially through the polymeric material of the body; at least oneelectrical conductor contained wholly within the polymeric material ofthe body at least in a region of the at least one transversely extendinghole; and at least one coating of an electrically conductive materialapplied to an outer surface of the cylindrical body, the coatingcomprising a first layer of a metal-deposition catalyst applied to thebody and at least one further layer of a conductive material comprisinga metal overlying the catalyst, the coating defining an electricallyconductive surface which is in electrical communication with the atleast one electrical conductor via the coating being contained in, andextending through, the at least one transversely extending hole definedin the body, so that the coating, by extending through the at least onetransversely extending hole forms an electrically conductive path thatforms a point of contact between the electrically conductive surface ofthe coating and the at least one electrical conductor to define anelectrically conductive region on the elongate body.
 42. The electricallead of claim 1 in which the conductive surface of the at least oneelectrically conductive region forms a band electrode on an outersurface of the elongate body.
 43. The electrical lead of claim 42 inwhich the band electrode extends about the periphery of the elongatebody.
 44. The electrical lead of claim 31 in which the band electrodeextends about the periphery of the elongate body.
 45. The catheter ofclaim 41 in which the electrically conductive region forms a bandelectrode on an outer surface of the elongate body.
 46. The catheter ofclaim 45 in which the band electrode extends about the periphery of theelongate body.
 47. The electrical lead of claim 27 wherein the at leastone electrical conductor is positioned between the inner member and theouter member.
 48. The electrical lead of claim 47 wherein the electricalconductor comprises a plurality of electrical conductors helicallycoiled in the wall of the elongate body, the conductors being arrangedin groups.
 49. The electrical lead of claim 48 further wherein anelectrically conductive region is associated with each group ofconductors.
 50. The electrical lead of claim 49 wherein each conductiveregion forms a band electrode on an outer surface of the elongate body.51. The electrical lead of claim 50 wherein each electrical conductorcomprises at least one metal wire made from a material selected from thegroup consisting of: PFA, FEP, polyimide and polyurethane insulatedcopper wire(s) and copper alloy wire(s).
 52. The electrical lead ofclaim 51 wherein the electrically conductive material is at least onemetal selected from the group consisting of: platinum, metal alloys,stainless steel, copper and silver.
 53. The electrical lead of claim 52in which the at least one coating is flexible to form a flexible bandelectrode on the outer surface of the elongate body.
 54. The electricallead of claim 53 in which the elongate body is of a non-porous material.